1. Field of the Invention
The present invention relates to a method of packet transmission and a packet data communication system.
2. Description of the Related Art
In packet data communication used in high-speed transmission lines of which Local Area Networks (LAN) are representative, in order that packet transmission delay not become a problem, flow control by fourth level end-to-end protocol, of which Transport Control Protocol (TCP, RFC) is representative, generally employs a small window size. However, because window size is related to the memory capacity of a terminal, it is desirable to make the window size as small as possible and reduce the memory capacity.
However, in a large-scale network such as for connection of inter-LAN communication, the type of intermediate circuits are unknown. For example, in a interLAN connection in which connections are made by satellite circuits within the network, because circuit delay becomes great in parts, throughput will drop even though satellite circuits are high-speed if the window size is small. FIG. 1 shows an example of the problem of throughput drop in a satellite LAN connection. If the window size is small, the delay in the satellite circuit cannot be absorbed and, as shown in FIG. 1, the throughput cannot attain the speed of satellite circuits. This problem of drop in throughput that occurs in the prior technology can be solved by enlarging the window size, but this solution gives rise to a problem of the increase in memory capacity.
If circuits having great delay time exist as a portion of a communication circuits, this type of memory increase must be carried out at all terminals that may use that circuit, and this poses difficult problems for network design.